1. Field of the Invention
The present invention relates to a glass-made lid for use with a cooking pan, pot, and the like, and a method of manufacture thereof. The glass-made lid allows the user to check to see how the cooking is occurring.
2. Description of the Prior Art
When a cooking pan, for example, is used for any cooking purpose, the pan is usually covered with its lid during the cooking process. Whenever it is required to check to see how the contents are being cooked, the lid must be removed from the pan. As this is inconvenient, it is desirable that the contents being cooked inside the pan can be monitored from the outside without removing the lid.
In order to meet the above needs, there are already glass-made lids that have been offered in a variety of kinds. For practical uses, those conventional glass-made lids have a different construction:
(1) one lid is made of a round sheet glass base formed to present a curved or bulged surface having its peripheral edge fitted with an annular metal ring;
(2) another lid is made of a metal base formed similarly and having an small see-through glass window mounted usually around its central area; and
(3) a third lid is totally made of a molded glass.
The above-listed conventional lids have their own problems including those involved in the process of forming the respective lids and therefore those associated with the products obtained through the respective forming processes. Specifically, the problems may be listed for each of those lids, as follows:
(1) The first-mentioned lid, which is formed to provide a bulged surface having a metal ring mounted around the peripheral edge thereof, may have a good visibilty and may be obtained through a relatively simplified process. However, the presence of the peripheral metal ring has a problem in several respects. As the contents are being boiled inside the pan, part of them, such as soup, may be flooded over, entering the joint between the peripheral edge of the glass base and the metal ring. That portion of the substances which has entered the gap between the two parts cannot be removed by the usual water cleaning, and remains there permanently as dirty solids. This raises a hygienic problem as well as an appearance problem.
(2) The second-mentioned lid, which consists essentially of a formed metal base with a central glass window mounted, provides a narrow scope of sight into the pan. It is apparent that as this limits the sight, it is impossible to see the interior of the entire pan. This construction also has the similar problem as described in the item (1) above, since it allows part of the boiling-over soup to enter the joint where the glass window is mounted, and produces the same hygienic problem.
(3) The last-mentioned lid, whose construction is totally made of an appropriately molded glass, may be advantageous over the first two constructions in that it has no problems as described above. Instead, there is a different problem associated with its forming process, which employs a particular metallic mold. The problem is that the glass lid obtained by molding usually presents irregularities on its surface, and an image may be viewed as distorted when the contents are seen through the lid. Furthermore, the glass material must be molded to a shape that can meet the particular requirements for the shape of a pan on which the lid is to be seated. Specifically, a sheet glass must be molded to the shape having a peripheral edge that exactly and snugly fits the corresponding peripheral edge of the pan when the lid is seated on the pan. Thus, a metallic mold must meet the particular dimensional and shape requirements. This requires a complex mold, which costs highly. Usually, the molding process must be followed by a tempering process so that the molded glass can have more strength. For the practical purposes, however, it is difficult to pass the molded glass through the tempering process, because any kind of lid is not thick enough to sustain the tempering process. Thus, the molded glass is usually finished as a product by bypassing the tempering process. If the tempering process is required so that the molded glass can have the practical strength requirements, it will have to have a greater thickness, which would make the lid heavier and less transparent.